Citing government officials and other people familiar with the activists' situation, the US publication said Saud al-Qahtani, a close adviser to Crown Prince Mohammed bin Salman (MBS), had overseen "some aspects of the torture", threatening one of the activists with rape and death.

Members of the commission began questioning some of the detainees over the past month in Jeddah's Dabhan prison, including 29-year-old activist Loujain al-Hathloul.

Citing government officials and other people familiar with the activists' situation, the US publication said Saud al-Qahtani, a close adviser to Crown Prince Mohammed bin Salman (MBS), had overseen "some aspects of the torture", threatening one of the activists with rape and death.

A former adviser at the royal court, Qahtani was dismissed in the aftermath of the killing of Saudi journalist Jamal Khashoggi at the kingdom's consulate in Istanbul on October 2.

Qahtani, who directed the crown prince's media operations, was one of 17 Saudi nationals sanctioned by the US Treasury Department in connection with Khashoggi's murder.

Members of the commission began questioning some of the detainees over the past month in Jeddah's Dabhan prison, including 29-year-old activist Loujain al-Hathloul.

"Saud al-Qahtani threatened to rape her, kill her and throw her into the sewage," one of the sources privy to the testimony told the newspaper.

At least eight of a total 18 activists have been subjected to some form of physical abuse, it said.

Other victims of torture include Aziza al-Yousef, a 60-year-old university professor, Eman al-Nafjan, a mother of three, and Samar Badawi, whose brother Raif Badawi has also been detained on charges of "insulting Islam".

Accountability measures

Lynn Maalouf, Middle East research director at Amnesty International, told Al Jazeera if reports of the investigation taking place are true, it is important that the commission's work is carried out in an impartial and transparent way.

"We need to know that the families of the activists are in the know of the process of the investigations, how this is being reported on, and any steps that are going to be taken afterwards based on the findings - so that means any accountability measures," said Maalouf.

"People who have been found responsible for these abuses should be held accountable and redress for the victims."

Formed under the leadership of the late King Abdullah in 2005, the human rights commission's work, which has avoided highlighting politically sensitive issues in public, is unlikely to lead to criminal charges.

"I don't see how they will hold anyone accountable if they already publicly denied that the torture ever happened," said one of the Saudi officials who is aware of the commission's work.

The Saudi government has dismissed the allegations as "wild claims" and denied security officials tortured the detained activists.